Typically one has OCT scans being done in a localized region of the eye with the result of the localized scan being displayed. In addition to this data from a localized area there are also other modalities that image a larger area of the eye or that image the eye in a different way, for example monochrome and color photography or laser scanning. It would be useful for the clinician to be able to look at those other modality images, and be able to see the OCT scans captured from another machine in alignment with the images.
The purpose is to allow the clinician can look at multiple exams of the patient's eye integrated into one screen. One of course one could display the images from different machines on different screens, but it is more helpful to the clinician to actually see the scans from the OCT and know which region of the eye they correspond to, as well as being able to see those features captured in a different way.
Thus in order to obtain the maximum amount of diagnostic information from all of these tests, there is a need for superimposing the images and the data associated with them. In short there is a requirement to compile them on top of one another and superimpose them together.
It is noted that the OCT scan provides valuable three dimensional cross sectional images of the eye which means one can see into tissue that is not visible just by observation. Thus, typically what happens is that during an OCT exam one can image a small area very densely but it takes quite a bit of time. Thus, there are limits on how much data one can process in one exam.
So typically what happens for instance if someone wants to image the macula one images a small region around just the macula. If someone has a problem with an optic nerve one images just a small region around the optic nerve. The trouble is that one is currently unable to look at all of the different areas together at one time. One can either look at the exam on the optic nerve or look at the exam on the macula. As a result there is a need for the ability to look at one large image of the eye and then to see all the different scan locations together on one screen.
In the past there have been a couple of attempts with correlating images and this is usually done by generating what is called an enface image. In taking an enface image one takes the depth scans of the dense OCT data and generates the enface image or a summation image. This means one uses the B scans and provides a calculated summation to create an image, namely a forward facing image from that data which looks like a photograph or an image one would see looking at the eye, but the resolution is very low and of very low quality. A lot of times it can have motion induced artifacts as the patient moves his eyes during the examination with the result that one does not obtain good resolution. So for instance in the middle of the scan the patient may be looking forward and then halfway through the scan their eye makes a quick movement to the side or up and down. As a result, The OCT can have a gap in it and the data can be misaligned so when one creates that enface image it's not real. It has errors in it and it presents an issue when one tries to register that feature or data against the other image of the eye to try to find the location where it fits.
In order to solve this problem in the past clinicians would create these summation images and they would try to register them manually against another image of the eye. However, when one has such errors, it makes it very difficult to align the blood vessel patterns. If the blood vessel patterns do not match, automatic alignment will fail.
Also just being an enface image, the resolution of the OCT scan is always lower than the actual resolution of the reference image so it is difficult to get a good alignment, especially if there are no very clear structures that are visible to the eye.